The effects of complexing agents with carboxylic and/or amine functional groups on the dissolution and polishing of copper in the presence of normalH2normalO2 were investigated as a function of pH. For this purpose, copper coupons were immersed in solutions of acetic acid, glycine, or ethylenediamine containing 5wt%normalH2normalO2 , and the loss of weight was determined gravimetrically. Analogous experiments were also carried out using copper oxide powders. The obtained results were then compared with polish rates of copper using slurries, containing silica as abrasives, in otherwise the same experimental conditions. While both sets of results were quite sensitive to the complexing agents used at different pH values, excellent correlation in trends was established between dissolution and polish rates.

Polishing slurries used in chemical-mechanical planarization ͑CMP͒ of copper typically include a complexing agent and an oxidizer. Our present work investigates the effectiveness of citric acid as a complexing agent for Cu with H 2 O 2 employed as an oxidizer. We show that the rate of copper removal from Cu increases when both citric acid and H 2 O 2 are used in acidic solutions ͑pH 4.0͒ and decreases drastically in alkaline solutions ͑pH 8.0͒, as well as in citric acid without any H 2 O 2 in the slurry. We investigate the underlying surface reactions of these effects by using Fourier transform electrochemical impedance spectroscopy ͑FTEIS͒ in combination with potentiodynamic measurements. We analyze the relative roles of citric acid, H 2 O 2 , and solution pH in Cu removal, and develop a reaction scheme describing the surface chemistry of Cu in this system. The results presented here also demonstrate how FTEIS can be used for quantitative investigation of surface reactions in complex CMP systems.Copper damascene structures are now widely used in integrated circuits, and chemical-mechanical planarization ͑CMP͒ is the preferred planarization technique for fabricating these structures. 1-4 The polishing slurry used in CMP contains a number of additives that have different chemical functions. 2 For instance, typical copper polishing slurries contain an oxidizer to form porous unstable surface oxides, and a complexing agent to dissolve material from the sample surface in the form of water-soluble complexes. 1 Understanding the relative roles of these different chemical additives is crucial to developing efficient polishing slurries. Our present work is centered on this specific issue and probes the chemical effects of citric acid as a complexing agent in the presence of a commonly used oxidizer, H 2 O 2 .Though citric acid has been evaluated as a complexing agent for Cu-CMP slurries, 5-9 a fundamental understanding of the surface reactions of citric acid with Cu at different pH values and/or oxidizer concentrations is still lacking. Our goal here is to probe these reactions in detail. As we have recently demonstrated, 10,11 Fourier transform electrochemical impedance spectroscopy ͑FTEIS͒ is an ideally suited technique for quantitative investigation of multistep reactions in CMP systems. FTEIS allows for fast ͑time-resolved͒ detection of impedance spectra 12-16 and hence, is particularly useful for studying transient corrosion effects. In this approach, circuit models of the reactive interfaces are obtained through rigorous complex nonlinear least square ͑CNLS͒ analysis of voltage and/or solution-dependent impedance spectra. 10,11 Subsequently, detailed reaction schemes are derived by comparing the CNLS analyzed results with those of potentiodynamic polarization measurements. 10,11,17,18 In this work, we utilize these capabilities of FTEIS in combination with standard CMP and potentiodynamic measurements to study pH-dependent surface chemistries of citric acid and H 2 O 2 on Cu. We demonstrate here that citric acid ac...

Oxalic acid was investigated as a complexing agent in H 2 O 2 -based slurries for chemical mechanical planarization ͑CMP͒ of Cu. At pH ϳ 1.5, oxalic acid acts as an inhibiting agent by forming an easily abraded soft bluish film on the copper surface. The high removal rate and low dissolution rates make it a desirable complexing agent, except for the strongly acidic pH condition. In the pH range 2.0-6.0, oxalic acid etches copper with the maximum dissolution rate occurring at pH ϳ 3.0. Cu removal rates and some electrochemical measurements that shed more light on these results are presented.As silicon semiconductor device feature size scales down to less than 0.5 µm, signal processing speeds are determined by interconnect delay. 1 The latter is a function of the dimensions of metal wires that interconnect different devices on a chip, the resistivity of the metal and the dielectric constant of the intermetal dielectric ͑IMD͒. The increase in this delay with a decrease in feature sizes can be overcome by decreasing the length of metal lines using multilevel metallization ͑MLM͒ structures, incorporating metals of low resistivity and dielectric materials of low dielectric constants. 2 Chemical mechanical planarization ͑CMP͒ has made the replacement of aluminum with copper, a metal with lower electric resistivity and better electromigration resistance than the former, feasible for all interconnections in advanced integrated circuits ͑ICs͒. Copper interconnections are fabricated using the damascene or the dual damascene process. 3 Successful fabrication of such interconnects requires the removal of the overburden Cu and barrier layer with minimal dishing of the metal lines and erosion of the underlying dielectric film. Optimization of the abrasive characteristics and the chemical composition of the slurry used to remove Cu and the barrier layer can help reduce the above defects.Cu CMP slurries typically contain sub-micrometer size abrasives dispersed in aqueous chemical solutions of oxidizing agents, complexing agents ͑etchants and inhibiting agents͒, and surfactants. 4 The complexing agents form complexes with the oxidized metal layer. They may etch the metal from its surface and/or dissolve the abraded metal debris ͑e.g., Glycine, 5 citric acid 6 ͒. They may also inhibit further oxidation of the metal surface by the oxidant and decrease the dissolution rates by forming a passivation layer, acting as an inhibiting agent ͑e.g., Benzotriazole 7 ͒. Both an etchant and an inhibiting agent are used in Cu CMP slurries to attain high removal rates and better planarity, respectively. Though considerable progress has been made in exploring different chemicals as additives in Cu CMP slurries, 4-14 a comprehensive understanding of their interactions would help not only in designing better CMP slurries but also in determining the factors that contribute to defect formation.Oxalic acid is an inexpensive, environmentally benign bicarboxylic compound that can form complexes with copper. 15 Its potential as a complexing agent in coppe...